Mass storage devices such as hard disk drive systems generally include a magnetic storage media for storing information, a spindle motor for rotating the storage media, a magnetic read/write head for reading information from or writing information to the magnetic storage media, and an actuator for positioning the read/write head over the storage media. A control system associated with the actuator controls the movement of the actuator.
An actuator in a hard disk drive system places the read/write head in an appropriate location over the magnetic storage media before a read or write operation occurs. Moving the read/write head takes time, though, and during that time the mass storage device cannot store or retrieve information. The average time required for the actuator to move the read/write head is referred to as the "seek time" of the storage device. Shorter seek times are preferable to longer seek times.
In moving the read/write head from one position to another, a conventional control system is modeled as a second order system. A problem with conventional control systems is that the second order system model produces a seek time that may be too long for modern applications. The time it takes for the read/write head to move from position to position is longer than desired, which causes the storage device to operate at a lower level of performance than desired.